1. Field of the Invention
The present invention relates to a master cylinder apparatus with a booster that augments the stepping force on a brake pedal of a vehicle.
2. Discussion of the Related Art
Heretofore, there has been known a so-called pull-type master cylinder apparatus with a booster that augments the stepping force on a brake pedal of a vehicle to generate boosted brake fluid pressure by pulling a pull rod connected between the brake pedal and a control valve for regulating air flow to and from the booster, as described in Japanese unexamined, published application No. 56-154357 (1981-154357) and No. 2001-294138. In the first known apparatus, the booster includes a booster shell comprising front and rear shells that sandwich a periphery of a diaphragm to divide the interior of the booster shell into constant-pressure chamber and a variable-pressure chamber. The control valve that regulates the communication of the variable-pressure chamber with the constant-pressure chamber and the atmosphere is provided in a piston that is attached to the diaphragm. The booster is attached to a master cylinder that comprises a cylinder body and a master piston. The cylinder body is provided with a cylinder that opens to a front surface of the cylinder body to which the booster shell is air-tightly fixed. The master piston is slidably inserted in the cylinder and has the rear end thereof entering a constant-pressure chamber of the booster to make abutting engagement with an output member of the booster. A reaction force generating device is interposed between the piston and the output member to make a reaction force act on the pull rod. The pull rod is connected to the brake pedal at the one end and is connected at the other end to a valve body of the control valve through holes made in the cylinder body, the master piston and the piston respectively. And the pull-type master cylinder apparatus with the booster is disposed in a engine room, and the rear end surface of the master cylinder is brought in abutment with a front surface of a dashboard of a vehicle to be attached thereto.
However, in the first prior art pull-type master cylinder apparatus with the booster, as the pull rod connected to the brake pedal is connected to the valve body of the control valve through holes that are respectively made in the cylinder body, the master piston and the piston, it is disadvantageously required to use many seal members, which results in complication in configuration. In addition, the whole length of the master cylinder apparatus becomes long to worsen the flexibility in mounting the master cylinder apparatus on the vehicle, because the pull rod extends from the front end of the cylinder to the rear end of the booster through the holes made on the axis thereof. It also worsens th flexibility in mounting the master cylinder apparatus on the vehicle and makes the master cylinder apparatus to be prone to vibrate that the booster with a large diameter is fixed to the front end of the master cylinder which is attached to the dashboard at the rear end thereof in an engine room.
In the second prior art pull-type master cylinder apparatus with the booster, the booster is attached at the rear end thereof to the dashboard in the engine room, and the master cylinder is fixed to the front and of the booster.
In the second prior art pull-type master cylinder apparatus with the booster, as the rear end of the booster is attached to the dashboard to mount the master cylinder apparatus on the vehicle, the stepping force exerted on the brake pedal acts on the booster, therefore the booster shell of the booster is made thick to have enough strength to prevent the deformation thereof. This makes the booster or the master cylinder apparatus heavy and expensive.